Transactions of the Illinois State Academy of Science received 1/4/00 (2000), Volume 93, #4, pp. 261-270 accepted 10/2/00 Seed Bank Ecology of Butterfield Creek Watershed Along Old Plank Road Trail Matthew S. Lake, Peter Gunther*, Deann C. Grossi, Holly L. Bauer Division of Science Governors State University University Park, IL 60466-0975 *Project Director (e-mail address: [email protected]) ABSTRACT Butterfield Creek watershed in Matteson, Illinois includes a wetland whose seed banks are of particular interest because of the presence of Old Plank Road Trail (OPRT). The trail runs from east to west bisecting the surrounding area into north and south wetland habitats. The resulting fragmentation of this landscape provides an interesting opportunity to investigate the effect of landscape fragmentation on seed bank ecology. The objective of this research was to determine any differential in seed bank composition related to landscape fragmentation resulting from OPRT. We removed a total of 60 core samples (30 from each side of the study area) representing three sequential depths, 0- 15cm, 15-30cm, and 30-45cm respectively. Core samples were transported to the labo- ratory for comparative determinations of seed bank germination. Results indicate that there is a discontinuity in the composition of the north and south seed banks as a function of soil depth. Landscape fragmentation brought about by the construction of the railroad (ca.1855, Molony and Ogorek, 1998) and back-flooding of the south side of Butterfield Creek caused a cessation of seed bank formation on the south side, which appears to be a remnant of pre-railroad vegetation seed deposition. Landscape fragmentation related to wetlands can result in the formation of seed bank remnants, which may provide valuable information about the dynamics of seed bank ecology in general as well as local vegeta- tive history in particular. INTRODUCTION Butterfield Creek watershed in Matteson, Illinois includes a wetland whose seed banks are of particular interest because of the presence of Old Plank Road Trail (OPRT). The trail runs from east to west bisecting the surrounding area into north and south wetland habitats. The resulting fragmentation of this landscape provides an interesting opportu- nity to investigate the effect of landscape fragmentation on seed bank ecology. A seed bank is a reservoir of viable seeds capable of replacing adult plants that may be annuals or perennials, susceptible to death by disease, disturbance, or consumption by animals, including humans (Baker, 1989). Seeds incorporated into seed banks have been recorded to have viabilities ranging from a single season to well over a thousand years 262 (Roberts, 1972 and Gunther et al., 1984). Generalizations to be drawn from the literature on seed banks suggest that extended seed viability is characteristic of disturbed habitats and also of aquatic plants where conditions may inhibit seed decay (Harper 1977). The ecological significance of seeds incorporated in a seed bank is related directly to their viability (Harrington, 1972 and Gunther et al., 1984). Recovery of these viable seeds can be beneficial in determining community composition and may indicate the relative sequence of seed deposition. Differences between seed banks in terms of species compo- sition can reflect ecological changes during seed bank formation. We suspect that land- scape fragmentation caused this kind of change to occur in the two wetland areas adjacent to Butterfield Creek, and that it is reflected in their respective seed banks. The Butterfield Creek watershed has received considerable attention in recent years due in large part to the activities of the Butterfield Creek Steering Committee and the forma- tion of The Old Plank Road Trail (OPRT) recreational path. Partial funding for the pur- chase of the OPRT wetland was secured through an Illinois Department of Natural Resources 2500 grant channeled through the Thorn Creek Ecosystem Partnership, a watershed-based consortium of which the Butterfield Creek Steering Committee is a member. The OPRT recreational path is built on an old railroad embankment, which fragmented the area into two ecologically distinct north and south habitats. This research focused on the potential effects of this landscape fragmentation on seed bank development in the area. The specific objective of the research was to determine any differential in seed bank composition related to landscape fragmentation resulting from OPRT. The null hypothesis is that landscape fragmentation does not cause differ- ences in adjacent seed banks. DESCRIPTION OF STUDY AREA The seed banks included in our study are part of a wetland located along The Old Plank Road Trail (OPRT) in Matteson, Illinois (Figure 1). Specifically, the wetland is located 283 meters west of Central Avenue in Rich Township and is bisected by OPRT. The Trail was an abandoned railroad prior to recent conversion into a paved recreational walkway and nature preserve, which runs west from Chicago Heights and, at its comple- tion, will end at the city of Joliet. It is the result of collaborative efforts from many town- ships and organizations to restore, preserve and utilize this tract of land stretching more than 12km. The Trail itself is approximately 2.5m wide and elevated 3-4m above the wetland surface. The introduction of the railroad resulted in a fragmentation of the land- scape, which is maintained by the presence of OPRT (Kalisz et al., 1997). The soil sur- face on the south side slopes away from the Trail so that, the water depth (July 1997) is approximately 0.75m near the railroad embankment, and increases to about 1.2m at the southern edge of the study area (Figure 2). The water depth on the north side, however, is relatively even at approximately 0.75m from the railroad embankment to the northern edge of the study area. A dense and extensive stand of Typha latifolia occurs on the north side of this elevated trail but is virtually non-existent on the south side. Seeds from the north population may be deposited in the seed bank on the south but are prevented from germination by current conditions. Also, fragmentation of the wetland may have changed the surface vegetation 263 resulting in two different seed banks. Development of the seed bank on the north side may have been influenced by the presence of more recent seed deposits of T. latifolia. On the other hand, the seed bank on the south side may contain remnant plant communi- ties extant prior to the introduction of the railroad. In order to investigate these alterna- tives, we conducted a comparative study of the north and south seed banks of the wet- land. MATERIALS AND METHODS Each core was separated into three vertical segments referred to as core samples (0-15cm, 15-30cm and 30-45cm). These segments were selected based on previous studies (Kalisz, et al., 1997 and Gunther, et al., 1984), which showed an exponential decrease in viability of seeds with respect to depth. This decrease would mean that seed banks are by no means vertically homogeneous and actually should be treated as different populations as a function of depth. Core Sample Collection Core samples were collected using a posthole digger (14cm diameter) during July 1997. Ten coring sites were selected from each side (north and south) of the wetland. Desig- nated coordinates for the coring locations were determined using a table of random num- bers. The resulting coordinates identified coring locations within a 9m2 grid constructed of electrical conduit and string. Thus the total of twenty coring sites (ten from each side) yielded a total of 60 core samples for seed bank analysis. The volume of each sample was approximately 2300cm3. Each core sample was placed directly into a clear plastic bag. Air was removed from each bag prior to labeling and sealing. In order to prevent additional light exposure, samples were further sealed in opaque white plastic bags from which residual air was removed. This process helped to ensure preservation of seed dor- mancy until exposure under laboratory conditions. The sealed samples were stored in darkness at 20 Co for 5 days and then transported to the laboratory experimental area. Experimental Design The experimental area consisted of a light canopy (1.6m x 2.3m) suspended 0.92m over a table of equal dimensions. Light intensity readings underneath the canopy ranged from 7800- 8800lux. Due to the pattern of light intensity variation, a randomized complete block design was used. Of the 60 core samples collected, 54 (27 from each side) were randomly selected for experimentation. Six core samples, 3 from each side, were retained in storage conditions for contingency purposes. The remaining core samples were placed into transparent plastic containers (17x28cm) and randomly assigned into three blocks in the experimental area (18 core-samples per block). Each container was covered with clear cellophane having openings at each end to prevent contamination from air borne spores while allowing for gas exchange. To maximize treatment exposure to light and air, core samples were repeatedly scored along their length and width (Gunther, et al., 1984). Treatment consisted of exposure to light and air for 70 days from July 21 to September 28, 1997. Relative humidity and ambient temperature were monitored within the experimental area using recording hygrothermographs (NovaLynx Corporation, model#225-5020A) cali- brated to mercury max/min thermometers (Taylor and forced-air psychrometers, 264 model#H331, Weather Measure Corporation). The temperature regime under the canopy was maintained at 30- 32C° as a minimum and 32- 36C° as a maximum. Daily maximum and minimum humidity ranged from 98-67% and 86-50%, respectively. Average diurnal maximum and minimum humidity was 82% and 63%, respectively. Numbers and identities of germinating seeds within each sample were recorded daily. These data provided a basis for characterizing any differences in the seed banks between the north and south sides of the trail.